Magnetic drive for bioreactor

ABSTRACT

The system and method of the invention pertains to use of a back iron on one or both ends of the impeller to increase the magnetic field density, and thus strengthen the magnetic coupling. In addition, pie-shaped (i.e. wedge) magnets, or variations thereof, increase the utilization volume and hence provide higher torque to allow the use of less expensive material (e.g. ferrites). In another embodiment, the rotor side is constructed with a Halbach array which increases the torque without the need to add a back iron piece. In another embodiment, an axial flux stator is implemented to replace the drive-end magnets and the drive motor.

FIELD

Embodiments relate generally to the field of bioreactors, and moreparticularly to a magnetic drive for a bioreactor.

BACKGROUND

Mixers and pumps have a wide range of applications includingbioreactors. The main elements in a mixer 100 (FIG. 1A) are the drive 14(which contains the driving mechanism) and the impeller 12 (whichcontains the mixing blades), at the impeller end 11. The two elementsare coupled together by different topologies. In one aspect, themagnetic coupling is where the impeller 12 holds a set of magnets 10that are coupled to the drive end 13. This is established by a set ofmagnets in the drive end rotated by a separate motor. The existingtechnology contains a set of cylindrical magnets 14 (See FIG. 1B) oneach end separated by a certain “magnetic” gap 16 which is primarilycomposed of air, fixing elements, and mixing bag wall which are allnon-magnetic elements. The existing technology suffers many impediments,including, but not limited to: (1) the weak coupling between the magnetswhich requires using more expensive and larger magnets (e.g., Neodymiummagnets), (2) poor volume utilization, (3) the use of rare-earth magnetsin the impeller which is a single use element that increases the cost ofthe impeller and poses environmental challenges, and (4) large drivesize, as it constructs of a set of large coupling magnets driven by aseparate electrical motor.

Mixing systems often include an agitator or impeller mechanicallyconnected to a drive shaft lowered into a fluid through an opening inthe top of a vessel. The drive shaft is connected to an electric motorarranged outside the vessel. In a closed vessel, a fluid seal isprovided between the drive shaft and the wall of the vessel to preventleakage of fluid from the vessel. Other mixing systems include arotating magnetic drive head outside of the vessel and a rotatingmagnetic impeller as an agitation element within the vessel. Themovement of the magnetic drive head enables torque transfer and thusrotation of the magnetic impeller allowing the impeller to mix andagitate the fluid within the vessel. Because there is no need in aclosed vessel to have a drive shaft penetrate the vessel wall tomechanically rotate the impeller, magnetically coupled systems caneliminate the need for having fluid seals between the drive shaft andthe vessel. Magnetic coupling of an impeller inside the vessel to adrive system or motor external to the vessel can eliminate contaminationissues, allow for a completely enclosed system, and prevent leakage.

Increasingly, in the biopharmaceutical industry, single use ordisposable containers or vessels are used as close type systems,typically in range of about 1-2000 liters. The vessel may be a tank-typesupport with for example substantially cylindrical shape and is made ofrigid material such as stainless steel to provide sufficient support forthe flexible bag or container, for example of a kind used in single-usebioreactors. Use of sterilized disposable bags eliminates time consumingsteps of cleaning of the vessel and reduces the chance of contamination.The flexible container or bag is placed inside the vessel in an accuratemanner so that for example different pipelines or tubes, mixers andsensors can be connected to the bag properly and accurately.

Combining the single use or disposable bags with a magnetic agitatorsystem establishes a sterile environment that is utilized inbiopharmaceutical manufacturing. A variety of vessels, devices,components and unit operations for mixing and manipulating liquidsand/or for carrying out biochemical and/or biological processes areavailable. For example, biological materials including mammalian, plantor insect cells and microbial cultures can be processed usingbioreactors that include single-use processing bags. Manufacturing ofcomplex biological products such as proteins, monoclonal antibodies,etc. requires, in many instances, multiple processing steps ranging fromfermentation or cell culture (bacteria, yeast, insect, fungi, etc.), toprimary recovery and purification.

It is desirable to address the needs as stated above by utilizing lessexpensive elements that are more environmentally friendly. Aspects ofthe invention will run a much smaller impeller, and have a reducedmagnetic force that will allow the bag to be separated from the drivemore easily. Further, moving parts on the drive (user) end will beaddressed to provide safer mechanisms.

SUMMARY

The system and method of the invention pertains to a magnetic drive fora bioreactor mixer or pump that strengthens the magnetic coupling toprovide higher torque and replace the drive-end magnets and drive motor.Embodiments disclosed herein use a back iron on both ends to strengthenthe magnetic coupling as well as a pie-shaped magnets (“pie” shaped inthe sense of a wedge shape and format (i.e., triangular/trapezoidal havea wider outer edge and smaller inner dimension) to increase the volumeutilization and hence provide higher torque and allow the use of lessexpensive material (e.g. ferrites). In another embodiment, the rotorside is constructed with a Halbach array which increases the torquewithout the need to add a back iron piece. Another embodiment implementsan axial flux stator to replace the drive-end magnets and the drivemotor.

One embodiment of a system is utilized as bioreactor mixer, the systemcomprising: a rotating drive, a fixed shaft, an impeller capable ofrotating around the fixed shaft, a plurality of magnets positioned inone or more array formats, a first set of magnets in a first arrayformat positioned at a drive end adjacent the rotating drive and asecond set of magnets in a second array format positioned at theimpeller, and at least one plate including the first set of magnetspositioned thereon such that the first set of magnets are positioned ina concentric geometric configuration and individually shaped with awider outside dimension that narrows toward a center of the concentricgeometric configuration; wherein the second set of magnets are arrangedadjacent one another to augment a magnetic field on one side of thesecond array while cancelling the magnetic field to zero on an oppositeside of the second array to achieve a spatially rotating pattern ofmagnetization. In one aspect, the system further comprises an externalvessel into which at least a portion of the bioreactor mixer is placed.

In another embodiment, a system is utilized as bioreactor mixer, thesystem comprising: a rotating drive, a fixed shaft, an impeller capableof rotating around the fixed shaft, a plurality of magnets positioned inone or more array formats, a first set of magnets in a first arrayformat positioned at a drive end adjacent the rotating drive and asecond set of magnets in a second array format positioned at theimpeller, and at least a first plate including the first set of magnetspositioned thereon; wherein the second set of magnets are positionedwith a second plate comprising a material having magnetic permeabilitygreater than the magnetic permeability of air and sandwiched between thefirst set of magnets and the impeller, such that a magnetic fieldgradient is created between the first array format of the first set ofmagnets and the second array format of the second set of magnets.

In one aspect, the first plate comprises a material having magneticpermeability greater than the magnetic permeability of air. The firstset of magnets can be positioned in an array format geometrically shapedwith a wider outside dimension that narrows toward a concentric center.The second set of magnets can be positioned in an array formatgeometrically shaped with a wider outside dimension that narrows towarda concentric center.

Detailed descriptions of various embodiments are described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A (PRIOR ART) illustrates the magnetic drive for a bioreactormixer.

FIG. 1B (PRIOR ART) illustrates a magnetic coupling where the impellerholds a set of magnets that are coupled to the drive end, the set ofmagnets in the drive end rotated by a separate motor.

FIG. 2 (PRIOR ART) depicts a cross-sectional view of the magnetic fieldcoupling in a prior art system.

FIG. 3 depicts a cross-sectional view of the magnetic field couplingwhen using the individual magnet shapes and configuration as disclosedin embodiments herein.

FIG. 4A illustrates the rotor side constructed with a Halbach array inanother embodiment, the individual magnets adjacent one another withoutspacing to form a concentric magnetic arrangement.

FIG. 4B illustrates an embodiment including pie-shaped magnets,individually positioned, angled, and spaced in a magnetic arrangementaround a central axis.

FIG. 4C illustrates an embodiment of the invention including a back ironon both ends.

FIG. 5 depicts a cross-sectional view showing the magnetic coupling inembodiments disclosed herein when using the pie-shaped magnets and backiron.

FIG. 6 provides a comparison of magnets as utilized in embodiments ofthe invention.

FIG. 7 depicts a comparison of maximum torque for cylindrical magnetsusing different materials in one embodiment.

FIG. 8 depicts a comparison of maximum torque for cylindrical magnetswith back iron.

FIG. 9 depicts a comparison of maximum torque for pie-shaped magnets andHalbach array

FIG. 10 depicts a graphic illustration of the relationship of torqueversus current density for the axial flux stator in one embodiment.

FIG. 11 illustrates an embodiment of the invention from a perspectiveside view.

FIG. 12 illustrates an embodiment of the invention from a perspectiveside view.

FIG. 13 (a), (b), (c) shows analyses of varying the stator length.

FIG. 14 (a), (b), (c) shows an analyses of varying the current density.

FIG. 15 (a), (b), (c) demonstrates analyses of varying the slot pitch,and resulting torque.

FIG. 16A illustrates a perspective view of an embodiment of a toothwound axial flux stator.

FIG. 16B depicts a perspective top view of the axial flux stator of FIG.16A.

FIG. 16C depicts a perspective side view of the axial flux stator ofFIG. 16A.

FIG. 16D depicts a perspective side view of the tooth height of theaxial flux stator of FIG. 16A.

FIG. 16 E depicts an embodiment of a stator core described herein.

DETAILED DESCRIPTION

Various embodiments will be better understood when read in conjunctionwith the appended drawings. It should be understood that the variousembodiments are not limited to the arrangements and instrumentalityshown in the drawings.

The system and method of the embodiments disclosed pertain to a magneticdrive for a bioreactor mixer or pump that strengthens the magneticcoupling to provide higher torque and replace the drive-end magnetsand/or drive motor, as desired. Embodiments include magnetic shapes andarrangements as well, including pie-shaped magnets (“pie” shaped in thesense of a wedge shape and wedged format (i.e., triangular/trapezoidalhave a wider outer edge and smaller inner dimension), such that thewedges fit together to increase the volume utilization and hence providehigher torque, and further allow the use of less expensive material(e.g. ferrites). In one embodiment, the rotor side is constructed with aHalbach array which increases the torque. Embodiments disclosed mayutilize a back iron on one or both ends to strengthen the magneticcoupling. With the Halbach array, torque is increased without a backiron piece. Another embodiment implements an axial flux stator toreplace the drive-end magnets and the drive motor. Embodiments aredisclosed as follows.

Pie-Shaped Magnet Configuration

For comparison purposes, FIG. 2 depicts a cross-sectional view of themagnetic field coupling 201 in a prior art system between a drive endmagnet 202 and an impeller end magnet 204; The magnetic field density203 is the area represented there between. An embodiment disclosedherein is shown in FIG. 3 where pie-shaped magnets are utilized in themixer 300. A cross-sectional view shows a large increase in the magneticfield coupling 301, the increased magnetic field density 303 between thedrive end magnet 302 and impeller end magnet 304.

FIG. 4A depicts the rotor side of a mixer 400 with a Halbach array 402in one embodiment. The individual magnets 403 are adjacent one anotherwithout spacing to form a concentric magnetic arrangement of the Halbacharray 402. The pie-shaped impeller end magnets 404 are spaced apart andpositioned on a magnetic plate 405. The magnetic plate may be a backiron, any magnetic material, including but not limited to any materialof magnetic permeability greater than air. In one aspect, the magneticplate may be a high magnetic permeability allow such as cobalt, iron, orother magnetic material. A magnetic field density 401 is created by thespace remaining where the individual magnets 403 of the Halback array402 levitate above the impeller end magnets 404.

Back Iron at Impeller and Drive Ends

FIG. 4B illustrates an embodiment of a magnetic drive 410 includingwedged (pie-shaped) magnets 412 at a drive end 411 and wedged(pie-shaped) magnets 414 at an impeller end 413, each magnet 412, 414individually positioned, angled, and spaced in a magnetic arrangementaround a central axis 415. A magnetic plate 405 is positioned at theimpeller end 413 while a second magnetic plate 406 is positioned at thedrive end 411. The magnetic plates 405, 406 are a back iron, in oneembodiment, and may be any magnetic material, including but not limitedto any material of magnetic permeability greater than air. A magneticfield density 417 is created between the drive end magnets 412 andimpeller end magnets 414, thus increasing the magnetic coupling. Inanother aspect, the magnetic plate is a high magnetic permeabilityincluding materials including, but not limited to, cobalt, iron, orother magnetic material.

In one embodiment, as shown in FIG. 4C, a magnetic drive 420 includes animpeller end back iron 405 and drive end back iron 406. The cylindricalshaped magnets 418 are spaced around a central axis 419, and positionedat each end such that a magnetic field density 421 is createdtherebetween. The back irons enhance the magnetic coupling of themagnetic drive, thereby increasing torque.

As illustrated in FIG. 4C, back iron is placed in the shape of theimpeller above the drive end magnets and below the impeller end magnets.The back iron reduces the overall magnetic path in air, the magneticfield density 421, between the drive end and the impeller end magnets.As a result, the magnetic field density that couples the two endsincreases.

FIG. 5 depicts a cross-sectional view of a mixing system 500 showing themagnetic coupling 501 in embodiments disclosed herein when using thepie-shaped magnets and back irons, as described in FIG. 4B.

A comparison of magnets is shown in FIG. 6. Baseline torque is at about5.8 Nm with cylindrical shaped magnets as shown in FIG. 4C. Note that .. .

TABLE 1 Materials used for the magnets in the magnetic drive. Magnetprice Material Grade ($/kg) Rare Earth Sintered NdFeB N42SH 70 SmCo 28/787 Non-rare Earth Alnico Alnico 9 57 Ferrite C8B/AC12 8.5

-   -   Table 1: Materials used for the magnets in the magnetic drive.

FIG. 6 illustrates that the cost of non-rare earth materials, e.g.,Alnico 9 and C8B/AC12 (ceramic) are cheaper and have beneficialcharacteristics that align with the desired magnetic compositions,characteristics, and configurations described.

FIG. 7 is a comparison of maximum torque for cylindrical magnets(ϕ=0.75×0.75). By replacing Neodymium (Sintered NdFeB) magnets, andusing other non-rare earth magnets, while keeping the cylindrical shapesand arrangement, the torque production is greatly reduced.

In another aspect, back iron may be added on one of the impeller end orthe drive end. Back iron added at impeller and drive ends improvestorque production, as illustrated in FIG. 8. Specifically, FIG. 8demonstrates the comparison of maximum torque for cylindrical magnetswith back iron, as represented in FIG. 4C. FIG. 8 shows that maximumtorque produced by different types of magnets (e.g., N 38/15, SmCo 28/7,etc.) as a function of magnet geometry. The ferrite magnet grade FB12Hgives twice the amount of the torque produced without the back plate,while eliminating the use of rare earth magnets. Three of the magnetgrades are not able to produce the baseline torque of the rare earthmagnets.

Embodiments of the invention modify the shape of the magnets fromcylindrical to pie-shaped configurations. As shown in FIG. 9, theimproved impeller-drive design provides 2.5 times the torque without theneed for expensive Neodymium magnets. Ferrite magnet grade FB12H gives2.5 times the amount of torque produced without the back plate and themagnet pie shape. As demonstrated in FIG. 4B, and referenced in FIG. 9,a comparison is shown of maximum torque for pie-shaped magnets.

Halbach Magnet Array

As shown in FIG. 9, an embodiment of the Halbach impeller-drive designof FIG. 4A provides the desired torque without the need for expensiveNeodymium magnets. This arrangement of Halbach array and pie shapedincreases the torque produced by a factor of 3 which delivers thebaseline torque.

Axial Flux Stator

Embodiments of the invention provide an axial flux stator to reduce thedrive end size, as well as reducing the number of components, andincrease its reliability. FIG. 11 depicts an embodiment of the axialflux stator 110 without the shaft and bearing, and without the levermechanism as utilized in the prior art. The drive stator 111 ispositioned on an underside of the magnets 112 and has a control circuit113.

The electrical and mechanical components of the axial flux stator 110are adjusted to address challenges in the modified design. Inembodiments of the axial flux stator, the electrical componentscomprise: high current density (cooling), a higher number of slots toallow high count of slots per pole and hence the ability to choosevarious coil span (to suppress harmonics), longer slots resulting inhigher leakage inductance and lower power factor, and higher currentresults in higher flux thus accommodating a bigger tooth to avoidsaturation.

The construction of the axial flux stator 120 is depicted in FIG. 12 asan axial-type magnetic gear. A magnetic core 121 is positioned between ahigh speed rotor 125 (stator with high frequency) and a low speed rotor126. The magnetic core 121 has a number of slots 122 depending on thearrangement of the impeller magnets and windings. The magnetic core maybe laminated, powder type, or a taped core, as desired. A set ofwindings are shown in FIG. 12 as stationary steel segments 123, orstator teeth, with modulation slots 122. The set of windings may betooth-wound, distributed, or fractional windings, as well. Windings canalso be single or multi-layer, wave or lap windings, full or shortpitched windings. The stationary steel segments can have additionalslotting to accommodate magnetic gearing (e.g., Vernier type machine)with single or multi-stage gearing. The stator can also have additionalmagnets when using a Vernier type machine.

An analysis of the axial flux stator with distributed windings (e.g., an18 slot example) demonstrates that by increasing the stator length, ahigher current path results per slot; saturation of the teeth occurs andcauses increased harmonics (See FIG. 13). Increasing the stator currentdensity results in higher torque; again, saturation of the teeth occursand causes increased harmonics (See FIG. 14). And, by increasing thestator slot pitch, higher torque results while placing mechanicalconstraints on the innermost tooth width (See FIG. 15).

FIG. 16A illustrates an embodiment of a tooth wound axial flux stator160 with nine (9) slots 165 (See FIG. 16C), for exemplary purposes, andnot limitation. FIGS. 16B, 16C, and 16D depict perspective views to moreclearly illustrate the details of the axial flux stator 160. The statorcore comprises pie-shaped magnetic stator teeth 163 that extendvertically from the stator back iron 162. The stator core 170 can beformed from sintered powdered iron, ferrite, or machined from a coil ofmagnetic steel. Conductive windings 164 are wound around the statorteeth 163. The conductive windings are divided up into phases. Withineach phase winding, the sense, field direction, of the individual coilsalternates so that the application of phase current to the phase windingcreates a magnetic field that is directed vertically upward in one toothand vertically downward in another tooth. The flow of current throughthe conductive windings forms a magnetic field that flows through thestator teeth, across the air gap between the stator 160 and a rotor 161,interacts with the magnets 166 on the rotor, travels through the rotor161, and returns through a rotor magnet of opposite magnetic polarity,across the air gap between the stator and rotor, through anoppositely-excited stator tooth, closing through the stator back iron162.

As shown in FIG. 16B, the exemplary stator has nine slots 165 of widthof about 0.470 in; the inside diameter (a hollow core 171 with centralaxis 172) of the stator core 170 is about 1.575 in, and the outsidediameter of the stator core is about 3.250 in. The width of the slots,the core inside diameter, and core outside diameter are parameters thatdetermine the performance of the motor. FIG. 16C depicts the magneticstator core 170 including stator teeth 163 in combination with the baseback iron 162 and shows that the stator core is about 2.750 in height,but can vary in size, shape and dimension, as desired for a particularmixer. FIG. 16D depicts the height of the magnetic pie-shaped statorteeth 163, the height of which is shown here as about 2.500 in. Theheight of the stator teeth and the thickness of the stator back iron areadditional parameters determined during the design of the motor, and somay be varied in shape and dimension.

In another embodiment, as shown in FIG. 16E, the stator core 175 isdefined with conic teeth 176 and including a back iron 177. As such, thestator core may be modified and designed to provide operationalefficiency of a mixer.

FIG. 10 compares torque versus current density of the axial flux stator160 for gaps of about 0.32 inches and about 0.265 inches between thestator and rotor. More torque is produced for a given current densitywith the smaller gap. The efficiency is slightly greater for the smallergap since the current is smaller.

As demonstrated, the embodiments thus described address the problemspresented in the art. The cheaper impeller as described comprises amagnetic coupling improved by increasing the magnetic field density.Higher torque density is produced by optimizing the impeller magnet byway of material, shape, and back iron, individually or in combination.The rare earth magnets can be replaced by less expensive andenvironmentally friendly non-rare earth materials, such as Alnico andFerrite, for example. In addition, the large and oversized driveassembly used prior now can run a much smaller impeller. Further, themoving parts on the drive side, near the user have been repositioned toprovide a safer device overall.

Additional technical and commercial advantages are provided with themore reliable system that includes the axial flux stator; the axial fluxstator has a smaller drive, no moving parts, and reduced magnetic forceduring bag installation. While cost and availability of the magnets isan advantage with improving magnet shape and material, the efficiency ofthe magnetic coupling that increase torque is very useful for furtherintensification of the bioreactor, various mixing systems, and overallefficiency.

In use, for example, microbial fermentations utilize more agitation forsufficient mixing, gas mass transfer and heat transfer at the reactorwall. An improved device of the invention including the axial fluxstator improves user experience due to a less complex design. Not onlyis the design more compact than a drive with permanent magnets, but theinstallation and removal of the bag is improved as there are nopermanent magnetic forces that have to be overcome. Moving parts areavoided with consequences on machinery directive requirements, sealingand ingress protection to avoid prior standard design that utilized alever mechanism to separate the drive from the impeller such that thebag can be pulled out of the reactor bottom end piece.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope. Dimensions, types of materials,orientations of the various components, and the number and positions ofthe various components described herein are intended to defineparameters of certain embodiments, and are by no means limiting and aremerely exemplary embodiments. Many other embodiments and modificationswithin the spirit and scope of the claims will be apparent to those ofskill in the art upon reviewing the above description. The scope of theinvention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Moreover, in the following claims, theterms “first,” “second,” and “third,” etc. are used merely as labels,and are not intended to impose numerical requirements on their objects.

This written description uses examples to disclose the variousembodiments, and also to enable a person having ordinary skill in theart to practice the various embodiments, including making and using anydevices or systems and performing any incorporated methods. Thepatentable scope of the various embodiments is defined by the claims,and may include other examples that occur to those skilled in the art.Such other examples are intended to be within the scope of the claims ifthe examples have structural elements that do not differ from theliteral language of the claims, or the examples include equivalentstructural elements with insubstantial differences from the literallanguages of the claims.

The invention claimed is:
 1. A system to be utilized as bioreactormixer, the system comprising: a rotating drive; a fixed shaft; animpeller capable of rotating around the fixed shaft; a first set ofmagnets in a first array format positioned at a drive end adjacent therotating drive and a second set of magnets in a second array formatpositioned at the impeller; and at least one plate including the firstset of magnets positioned thereon such that the first set of magnets arepositioned in a concentric geometric configuration and individuallyshaped with a wider outside dimension that narrows toward a center ofthe concentric geometric configuration; wherein the second set ofmagnets are arranged adjacent one another to augment a magnetic field onone side of the second array while cancelling the magnetic field to zeroon an opposite side of the second array to achieve a spatially rotatingpattern of magnetization.
 2. The system of claim 1, further comprisingan external vessel into which at least a portion of the bioreactor mixeris placed.
 3. The system of claim 1, wherein the first set of magnetshave a slot formed between each individual magnet in the array format,the slot having a slot pitch.
 4. The system of claim 1, wherein thefirst array format of the first set of magnets has uniformity of slotwidth and magnet height.
 5. The system of claim 1, wherein the first setof magnets and the second set of magnets are comprised of rare Earthmaterials.
 6. The system of claim 5, wherein the rare Earth materialsinclude Neodymium and Samarium-Cobalt, individually or in combination.7. The system of claim 1, wherein the first set of magnets and thesecond set of magnets are comprised of non-rare Earth materials.
 8. Thesystem of claim 7, wherein the non-rare Earth materials include Alnicoand Ferrite, alone or in combination.